An important goal in present day design of electrical equipment is reduction in size: even when actual miniaturization is not attempted, space and volume reduction is considered desirable. One way to accomplish such reduction is to combine functions in a single device structure.
There are numerous situations where the work of the designer of electrical equipment is very seriously compromised by space limitations, particularly in connection with high performance installations for use in aircraft, guided missiles, and the like. A great deal of equipment must be positioned in the nose of a submarine torpedo, for example, if all of the control, target seeking, and like functions required from a torpedo are to be successfully accomplished. The envelope of the torpedo defines the available space, and the design problem is to produce the necessary equipment in such dimensions as to fit into that space.
This is particularly important in connection with components which by the nature of their function relative to sonar transmission or reception, for example, must be physically located close to the torpedo envelope. An obvious design step is to select circuit components which are as space efficient as possible, but another useful step has been found, namely, that of combining the functions of two or more circuit elements within a single physical body, where this can be done without greatly increasing the size of the body itself. Successful use of expedients such as this may make all the difference between a practical, useable piece of equipment, and an arrangement which is otherwise desirable, but cannot be fitted into the space available.